[TheForge] Re: Subject: Didymium? I say "no way."

[Mike Porter]

Bruce,
Any light in sufficient amounts will burn your eyes. It is true that the 
smaller the wave lengths, the greater the amount of energy they carry. This 
is why UV is more harmful than IR. However, they both have the same main 
hazard--they are invisible. You don't react to either UV or IR. There is no 
pupil contraction to either one of them, no blink reflex, no urge to look 
away, as there is with too much visible light. This has every bit as much to 
do with  physical impact as the square of the distance.

Also, only far range IR is felt as heat. Near range IR is not felt at all, 
just as green light isn't felt. So, if it packs so little energy compared to 
every other light band, what is the big deal? That there is so very much of 
it whenever anything is heated past 1000 degrees. The amount of energy that 
super heated objects put out as IR is huge before you ever see the faintest 
glow of visible incandescence. As they brighten into the visible range, the 
IR multiplies as well.

Lots of people can't just look away from the heat source. How do you braze 
or gas weld without looking at the heat source? How do you pound 
incandescent hot iron without looking at it? I'm not saying everyone should 
rush out and get protection from IR. That's your individual choice. I was 
originally answering a question asked by someone who does want that 
protection.
Mike P.
----- Original Message ----- 
From: "Bruce Freeman" <freemab222 at yahoo.com>
To: "theforge" <theforge at mailman.qth.net>
Sent: Thursday, February 09, 2006 6:45 PM
Subject: [TheForge] Re: Subject: Didymium? I say "no way."


> Unlike Mike, I have NOT intensely researched
> protective eyewear.  However, I have one pedantic
> correction to his posting, and one genearl issue.
>
> The pedantic correction is that the yellow "sodium
> flare" has nothing to do with soda reacting with air.
> Merely heating sodium to flame temperature is
> sufficient to produce the flare.  Okay - who cares!?
>
> The other observation is what I consider an excessive
> concern about IR radiation.  IR is translated to heat
> when it encounters anything that absorbs it.   If that
> thing then gets warm, it will retransmit IR.  Ordinary
> glass absorbs most IR, and many plastics do as well.
> You can tell if a lens absorbs IR:  place it in front
> of a heater and see if it gets hot.  Unfortunately,
> that will not tell you what wavelengths it absorbs,
> should that matter.
>
> The thing about IR is that it is the least likely
> radiation to get you in trouble -- because you can
> feel it.  If you're so "manly" that you refuse to look
> away from the fire as your face cooks, then your
> eyeballs will cook along with your face.  Remember the
> reverse-square law:  Twice the distance from the heat
> is 1/4 the heat intensity.  Pretty easy to avoid too
> much IR.
>
> None of this is to say that IR should be ignored.
> But, finding a clear material that would PASS IR has
> been a significant problem in science.  Ordinary salt
> (NaCl) works, as do the chemically -related salts,
> such as potassium bromide (KBr).  Even those start
> absorbing if they pick up water, so they have to be
> kept dry.
>
> Bottom line:  Don't be stupid and try to cook your
> face and eyeballs, and you'll probably have no problem
> with IR.
>
> UV is another ball of wax.  Never look at an arc, even
> briefly.  Even the reflection of an arc can be
> damaging.
>
> Bruce
> NJ
>
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